Often more content needs to be displayed on one “page” than will fit on a given screen. User interfaces overcome this by allowing users to “scroll” around a page in vertical and horizontal dimensions. However allowing users to scroll can create some additional problems. For example, at any given time a display needs to let the user know that they can scroll in a given direction. In that regard, the display needs to indicate whether a user may scroll up or down in the middle of a document, down at the top of a webpage, or left at the start of a spread sheet. The display may also need to inform the user of the current cursor position relative to the entire distance that can be scrolled. Additionally, a display may give the user “affordances” to actually scroll and manipulate the display (e.g. pressing “page down” key or click and drag the “thumb” on the scrollbar). Traditionally these problems have been overcome with traditional “scroll bars” at the side however these may be inadequate for a variety of reasons.
Traditional scroll bars use up valuable screen real estate and prevent the user from reading the content and monitoring the relative position at the same time. In the context of a mobile device the problem of screen real estate becomes even more critical because your physical screen is small (even if your resolution increases). Additionally, a user's eye must (and typically does) jump from the content in question to the scroll bar. This jumping of focus point back and forth slows down interaction and puts additional strain on the user's eyes.